Effects of repeated urea doses on soil chemistry and nutrient pools in a Norway spruce stand

Pools of macro-nutrients in soil and vegetation were studied in an old fertilization experiment with a large previous input of N. Different doses of N, in the form of urea, had been added four times during a 20-year period. In total, between 480 and 2400 kg N ha⁻¹ had been given. The experiment was established in a relatively productive Norway spruce stand and the expectation was that the large N input would cause an accelerated leaching of N, especially nitrate, accompanied by soil acidification and losses of several nutrients. The aim was to test for possible residual effects. Thirteen years after the last N addition, samples from the aboveground part of trees, field layer, S-layer, humus layer and mineral soil (0–10 cm) were analyzed for concentrations of most major nutrients. Nutrient pools were calculated. In the humus layer, the concentration of N increased and the C/N-ratio decreased with increasing N dose. The calculated recovery of added N in soil including ground vegetation was complete for the lowest N dose, while it was 25–50% for higher doses. The amount of N retained was unaffected by the N dose. The amount of extractable P in the upper part of the mineral soil was negatively correlated with N dose, as was also the concentration of total P in the S-layer. Neither soil pH, nor concentrations or amounts of Ca, Mg and K were affected by the previous fertilization. The calculated total soil-plant pool was only influenced by N dose in the case of P, which was 20% lower at the highest N dose compared with unfertilized conditions. Despite the large extra N input, the nutritional changes in plants and soil of the actual study site seemed surprisingly small.     

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden

Effects of irrigation and liquid fertilization on fine root (< 1 mm) production and longevity, and fine root (< 0.5-2 mm) biomass were studied in a Norway spruce (Picea abies (L.) Karst.) stand in northern Sweden. Fine root length production and longevity were measured by the minirhizotron technique at 0-10 cm depth in the following treatments: irrigation (I), liquid fertilization (IL) and control (C). Standing root biomass and root length density (RLD) were studied in the litter-fermented humus (LFH) layer and at depths of 0-10, 10-20 and 20-30 cm using soil cores in solid fertilized (F) and C plots. Minirhizotrons were installed in October 1994 and measurements recorded monthly from July to September 1995 and during the growing season in 1996. Soil cores were sampled in 1996. Fine root production increased significantly in IL plots compared with C plots, but the I treatment did not increase root production. Root mortality increased significantly in IL plots compared with C plots. Fine root longevity in IL plots was significantly lower compared with C and I plots. No significant difference was found between longevity of fine roots in I and C plots. Compared with C, F treatment increased fine root biomass in the LFH and mineral soil layers, and increased the amount of fine roots in mineral soil layers relative to the LFH layer. Furthermore, F increased RLD and the number of mycorrhizal root tips significantly.     

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden

The PEACH computer simulation model of reproductive and vegetative growth of peach trees (Grossman and DeJong 1994) was adapted to estimate seasonal nitrogen (N) dynamics in organs of mature peach (Prunus persica (L.) Batsch cv. O'Henry) trees grown with high and low soil N availability. Seasonal N accumulation patterns of fruits, leaves, stems, branches, trunk and roots of mature, cropping peach trees were modeled by combining model predictions of organ dry mass accumulation from the PEACH model with measured seasonal organ N concentrations of trees that had been fertilized with either zero or 200 kg N ha(-1) in April. The results provided a comparison of the N use of perennial and annual organs during the growing season for trees growing under both low and high N availability. Nitrogen fertilization increased tree N content by increasing organ dry masses and N concentrations during the fruit growing season. Dry mass of current-year vegetative growth was most affected by N fertilization. Whole-tree N content of fertilized trees was almost twice that of non-fertilized trees. Although N use was higher in fertilized trees, calculated seasonal N accumulation patterns were similar for trees in both treatments. Annual organs exhibited greater responses to N fertilization than perennial organs. Estimated mean daily N use per tree remained nearly constant from 40 days after anthesis to harvest. The calculations indicated that fertilized trees accumulated about 1 g N tree(-1) day(-1), twice that accumulated by non-fertilized trees. Daily N use by the fertilized orchard was calculated to be approximately 1 kg N ha(-1), whereas it was approximately 0.5 kg N ha(-1) for the non-fertilized trees. During the first 25-30 days of the growing season, all N use by growing tissues was apparently supplied by storage organs. Nitrogen release from storage organs for current growth continued until about 75 days after anthesis in both N treatments.     

Importance of soil extractable phosphorus distribution for mature Norway spruce nutrition and productivity

Phosphorus is an essential nutrient for forest growth. In this study, we assessed the impact of soil extractable phosphorus using two simple extraction methods on nutrition and productivity of Norway spruce in sixteen mature forest stands on different bedrocks and soils in Bavaria, Southern Germany. Representative trees were sampled for needles, twigs, branches, stem bark, and stem wood. Total phosphorus content in the tree parts and soil phosphorus stock extractable with citric acid and sodium bicarbonate up to a soil depth of 80 cm were determined. We found that easily soil extractable phosphorus is a suitable indicator for estimating phosphorus uptake and stand productivity in Norway spruce. In contrast, organic layer phosphorus showed no significant correlation with aboveground biomass phosphorus contents. In the biomass, the highest phosphorus contents were measured in young needles and twigs, but the highest correlation with soil phosphorus was detected for phosphorus contents in needles and bark. The stock of phosphorus extracted by citric acid down to 40 cm soil depth revealed the best correlation with phosphorus in needles and bark. Therefore, as a supplemental or alternative method to needle analysis, our study suggests the use of phosphorus contents in stem bark to evaluate tree phosphorus nutrition. These results highlight the suitability of the citric acid soil extraction method to characterize plant available phosphorus in Norway spruce ecosystems.     

Effect of soil chemical properties on growth,foliation and nutrition of Norway spruce stand affected by yellowing in the Bohemian Forest Mts., Czech Republic

In 1998, a fertilizer experiment aiming to investigate the effects of slow-release N, P, K and Mg fertilizer (SILVAMIX Mg NPK^®) on a 60-year-old spruce stand with symptoms of yellowing was established. In this paper, trees were selected to investigate the relation between annual diameter increment, yellowing, foliation, needle and soil chemical properties: ten from the fertilized treatment (F), ten green trees from the control (CG) and ten yellow trees from the control (CY). CG and CY trees were growing in close proximity at a distance of only several meters apart under the same soil conditions. In treatment F, increased annual diameter increment, improved foliation, needle Mg concentration, plant-available Mg and P concentrations in the soil and absence of yellow trees were recorded 7 years after a single application of the fertilizer. During the last 15 years, annual growth increment and foliation of CY trees have continuously decreased while relatively stable values were recorded for CG trees and increased for F trees. In 2006, CG and CY trees differed significantly in Mg concentration in needles, foliation, yellowing and annual diameter increment. Although differences in soil chemical properties between CG and CY treatments were not significant, lower concentrations of plant-available Mg²⁺ and higher concentrations of H⁺ and Al³⁺ were found in soils under CY trees. There was a negative correlation between soil concentration of Mg and yellowing, but this correlation was relatively weak, indicating that there is no simple relation between soil and needle concentrations of Mg. In the investigated locality, the “new type” of yellow tree decline has been a long-term gradual process.     

Effect of removal of logging residue on nutrient leaching and nutrient pools in the soil after clearcutting in a Norway spruce stand

Following clearcutting applying the conventional stem-only harvesting method in a Norway spruce (Picea abies (L.) Karst.) stand and different levels of removal of logging residue, the nutrient fluxes from the heaps of logging residue and from the O horizon were monitored over four growing seasons and the soil nutrient pools were determined. Three levels of removal of logging residue were carried out using (i) conventional stem-only harvesting (no residues removed); (ii) residues removed; and (iii) removal of branches (foliage left on site). The heaps of logging residue were a minor source of inorganic N entering the soil in the water percolating through the heaps, but they were a significant source of organic N, P, Ca, Mg, and especially K. Nutrient fluxes from the O horizon were in general greater under the heaps of logging residue as compared to soils without overlying logging residue. The leaching of inorganic N from the O horizon under the heaps of logging residue resulted in a net loss of these compounds, while the O horizon without overlying logging residue gained N. The removal of logging residue significantly decreased the extractable K pools in the soil while it or conversely, the presence of residue heaps had no significant effect on the pools of organic matter and the pools of N, P, Ca, and Mg in the O horizon and in the 0–10 cm soil layer. The results show that the short-term effects of logging residue on nutrient dynamics in the soil can be complex and difficult to interpret in terms of site productivity as there are changes in the nutrient fluxes, which imply the opposite effects on site productivity. However, the results do indicate that, in the short-term, the removal of logging residue does not impair pools of N in the soil nor site productivity on sites where the availability of N limits productivity.     

Response of litter decomposition and soil C and N transformations in a Norway spruce thinning stand to removal of logging residue

Increasing demand for production of bioenergy has led to an interest in forest management which uses logging residue from both clear-cuttings and thinning stands. The aim of this study was to investigate the effects of removal of logging residue in a thinning Norway spruce stand on (1) litter decomposition and (2) soil microbial processes in C and N cycling and the quality of soil organic matter. The study site was a 40-year-old Norway spruce stand growing on a relatively fertile site. During thinning, logging residue was either removed (whole-tree harvest) or left on the site (stem-only harvest). Different types of material in the logging residue, from main branches to needles, were weighed separately into mesh bags. The bags were placed above the moss layer in the whole-tree harvest treatment and in the logging residue layer in the stem-only harvest treatment, and decomposition was monitored for 5 years after treatment. From the humus layer, samples were taken 10 years after treatment. Harvest method affected the mass loss of the litter material very little but the C-to-N ratio of the remaining material was slightly higher in whole-tree harvest than in stem-only harvest, particularly in the needle material. In the humus layer samples, taken 10 years after treatment, the rate of C mineralization was lower in whole-tree harvest than in stem-only harvest; also the rate of net N mineralization and the amounts of C and N in the microbial biomass tended to be lower, although not statistically significantly. Removal of logging residue had no effect on pH (pHH₂O$\text{p}{\text{H}}_{{\text{H}}_2\text{O}}$ 3.9 in both treatments) or C-to-N ratio (28 in both treatments) in the humus layer. The concentrations of total water-soluble phenols and an important group of phenols, condensed tannins, were both lower in the humus layer of whole-tree harvest than in that of stem-only harvest. Concentrations of sesqui-, di- or triterpenes in the humus layer were similar in both treatments. In conclusion, 10 years after harvest, soil microbial activities and organic matter characteristics in whole-tree harvest differed from those in stem-only harvest.     

Effects of water availability and fertilization on nitrogen cycling in a stand of Pinus radiata

Nitrogen cycling was studied for four years (1983–1987) in an N-deficient 10-year-old stand of Pinus radiata growing on a yellow podzolic soil which had a low water-holding capacity. Trees were subjected to combinations of irrigation of N-fertilization resulting in a wide range of N uptake and tree growth. Net mineralization, plant uptake and leaching of soil N was monitored using a sequential coring and in-situ incubation technique. Nitrogen concentrations were measuredd monthly in live needles and litterfall. Average rates of weight loss and release of N from decomposing litter were estimated over a 3-year period using a budgeting approach.

Trees responded only to N (not to P, and there was no N×P interaction), but there was a large positive interaction between N supply and water availability. Response to fertilizer averaged + 24% over a 4-year period, but was zero during a growing-season which contained a 4-month drought. Irrigation alone increased growth by 60%, but in combination with high N availability growth increased 2–3 fold. Annual uptake of N ranged from <10 (irrigated plots in years 2 and 3 after enhanced mineralization during the initial year) to 166 kg ha⁻¹ (during a wet growing season following heavy N fertilization). Although soil mineral-N concentrations were elevated for only about 1 year after fertilization, fertilization enhanced rates of N mineralization throughout the soil N mineralization may have resulted from re-mineralization of the large quantity (147 kg soil N mineralization may have resulted from re-mineralization of the large quantity (147 kg ha⁻¹) of fertilizer N immobilized by the soil during the initial 8 months after fertilization, or the N released from decomposition of fine roots having higher N content. Nitrification was negligible in unfertilized soils, but increased markedly 50–100 days after fertilization and resulted in the leaching of about 60 kg N ha⁻¹ during autumn and winter of the first year after fertilization. Fertilized soils have continued to nitrify readily. Irrigation increased rates of weight loss and N release from decomposing litter.

The rate of N uptake by trees markedly affected the concentrations of N in newly emerging and older needles, and the concentration of N in needlefall. The weighted mean concentration of N in annual needlefall ranged from 0.42% in the irrigated-only plot (most N-stressed) to 0.94% in the heavily fertilized plot during the first year after treatment. These weighted concentrations are a useful index of N uptake from the soil and of growth rate where water supply is not limiting. Except for the initial year after heavy N fertilization, annual uptake of N was equivalent to annual soil N mineralization, and N uptake was positively linearly correlated with annual basal-area increment of trees.     

Influence of nitrogen and phosphorous availability and ozone stress on Norway spruce seedlings

Four-year-old Norway spruce (Picea abies L. (Karst.)) seedlings were exposed to ambient and elevated (1.5 x ambient in 1997 and 1.6 x ambient in 1998) ozone concentrations [O3] and three nitrogen (N) and two phosphorus (P) availabilities: "optimal" values (control); 70% of the control N and P values (LN and LP); and 150% of the control N value (HN). Treatments were applied in an open-field ozone fumigation facility during the 1997 and 1998 growing seasons. Effects on growth, mineral and pigment concentrations, stomatal conductance and ultrastructure of needles were studied. The HN treatment increased growth significantly, whereas elevated [O3] had a slight or variable impact on growth and biomass allocation in all N treatments. Although there were no significant effects of the LP treatment on plant growth during the second year, there was a reduction in 1-year-old shoot dry mass in the elevated O3 + LP treatment at the end of the experiment. There were no significant treatment effects on mineral concentrations of current-year and 1-year-old needles at the final harvest. In response to the HN treatment, chlorophyll a and b and carotenoid concentrations increased significantly in current-year needles. Chlorophyll a/b ratio decreased in response to elevated [O3] alone, but increased in seedlings in the O(3) + LP treatment. Stomatal conductance of current-year needles decreased with increasing N availability, but increased in response to elevated [O3]. However, the O3-induced increase in stomatal conductance was less in the LN and LP treatments than in the control treatment. In chloroplasts of current-year needles, increased N availability decreased mean starch grain area, but increased the number of plastoglobuli. We conclude that Norway spruce seedlings are relatively tolerant to slightly elevated [O3], and that nitrogen and phosphorus imbalances do not greatly affect the influence of O3 on this species when the exposure lasts for two growing seasons or less.     

Diachronic analysis of individual-tree mortality in a Norway spruce stand in the eastern Italian Alps

? Understanding tree mortality processes across time requires long term studies. Spatiotemporal patterns of mortality in a 200 years-old mono-layered Norway spruce stand were evaluated to determine what factors affected individual-tree mortality.

? We performed an analysis on two surveys (1993 and 2005) in a 1-ha permanent plot in the Paneveggio forest (Eastern Italian Alps). Tree diameter and age distribution between surveys were compared. We examined spatial patterns of living and dead trees before 1993, in 1993 and in 2005 using univariate and bivariate Ripley’s K(d) function, and a kernel estimator of local crowding. A logistic model was used to assess the effects of diameter, age, recent growth and competitive pressure on tree mortality.

? Spatial pattern analysis indicated mortality was associated to tree neighbourhood (neighbour effect at 2–5 m). An increment of regularization of tree spatial pattern occurred due to density-dependent mortality. Logistic regression showed tree diameter and recent growth were determinant on mortality risk during the monitoring period.

? Even if the stand is relatively aged, mortality dynamics are those typical of stem exclusion stage. Mortality was related to competitive dynamics, and small suppressed trees with slow growth rate had higher probability to die.

     

Characterization of glutathione S-transferases in needles of Norway spruce trees from a forest decline stand

Glutathione S-transferases (GST) detoxify many electrophilic xenobiotics, including several volatile organic compounds and pesticides. The GST activity for the conjugation of several xenobiotic substances was isolated from needles of Norway spruce (Picea abies L. Karst.) trees from a forest decline stand in the northern alps. Trees that exhibited different degrees of damage were selected from several stands in an altitude profile. The GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) in crude protein extracts of needles showed a seasonal pattern with highest activity during summer. The GST activity exhibited a strong dependence on the altitude of the stand showing highest activities in trees growing in the valley and lowest activities in trees growing in the summit regions of the mountain. When cytosolic GST from needles of healthy and damaged trees was purified, trees of healthy appearance exhibited three distinct GST isozymes with activities for the conjugation of CDNB and 1,2-dichloro-4-nitrobenzene (DCNB), whereas severely defoliated trees exhibited four GSTs with additional activity for the conjugation of ethacrynic acid. The main GST isozymes catalyzing the conjugation of CDNB differed in molecular weight, isoelectric point and catalytic properties between damaged and healthy trees.     

Hebeloma inoculation on Norway spruce seedlings in solarized and infested soil

The effect of inoculation of Hebeloma sp. on the growth of Norway spruce (Picea abies) seedlings was studied, in a controlled environment, with soil samples naturally infested by Pythium spp., Fusarium spp. and Rhizoctonia solani, and with samples of soil in which the pathogens had been controlled by solarization. The best results were obtained in solarized soil, but mycorrhizae also enhanced plant growth in the presence of the whole soil-borne mycoflora. The combined use of inoeulation of a mycorrhizal fungus and solarization is discussed.     

Wood volume yield and stand structure in Norway spruce understorey depending on birch shelterwood density

Wood volume yield and stand structure were investigated for Norway spruce understorey growing at 1500 trees ha⁻¹ under birch shelters of two different densities, 300 and 600 trees ha⁻¹, and Norway spruce growing without shelter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial.Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1.78 m³ ha⁻¹ year⁻¹ under the dense and sparse shelterwoods, respectively) was significantly lower than that of unsheltered spruce (mean annual increment 2.43 m³ ha⁻¹ year⁻¹). The loss in wood volume yield for sheltered spruce was more than compensated for by the additional wood volume yield in the shelterwoods (mean annual increments 3.26 and 1.88 m³ ha⁻¹ year⁻¹ for the dense and sparse shelterwood respectively).Shelterwood density did not produce any significant differences in inequality of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light.Immediately after trial establishment, trees in the no shelterwood treatment (i.e. where all overstory trees had been removed) showed a marked increase in diameter growth. Over time, the growth rate of unsheltered Norway spruce was reduced to a level comparable to that of sheltered spruce. The difference in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness index (h/d) with increased shelterwood density for the understorey trees.     

Impact of soil pressure and compaction on tracheids in Norway spruce seedlings

We tested the effect of soil compaction on Norway spruce seedlings in terms of the size and theoretical volume flow rate of the tracheids. The results show that soil pressure limits growth in the diameter of the lumens of tracheids in all parts of seedlings studied. The tracheids of the roots with primary xylem had larger lumens than those of the roots and shoots with secondary xylem in both unloaded and loaded seedlings. This corresponds to the higher cumulative theoretical volume flow rate of the tracheids from roots with primary xylem than those from roots and shoots with secondary xylem. Although the volume flow rate of tracheids, according to the Hagen-Poiseuille law, was directly proportional to the quadratic power of the capillary diameter (tracheid lumen), the cumulative curve of the theoretical hydraulic volume flow rate was higher or relatively comparable in loaded seedlings. An explanation for these findings is that there were higher gradients of water potential values in roots and leaves in loaded seedlings because the lengths of the conductive pathways were 27% shorter than in unloaded seedlings. We hypothesise that trees have adapted to different stresses by shortening their conductive pathways to maintain a transpiration rate similar to that of non-stressed trees. These results concerning the impact of soil compaction on tracheid diameter and volume flow rate improve our understanding of the growth and functioning of different conifer organs and the mechanisms underlying the efficiency of water transport through the root xylem to the shoot.     

Temporal variation and efficiency of leaf area index in young mountain Norway spruce stand

Temporal variation of leaf area index (LAI) in two young Norway spruce stands with different densities was monitored during eight consecutive growing seasons (1998–2005). We focused on: (1) LAI dynamics and above-ground mass production of both spruce stands and their comparison, (2) leaf area duration (LADU), crop production index (CPI) and leaf area efficiency (LAE) evaluation, and (3) thinning impact on the above-mentioned parameters. Also, we tried to deduce the most effective LAI value for the Norway spruce forest investigated. The LAI values of both spruce stands showed a typical seasonal course. To describe the LAI dynamics of the stand, we recommend taking LAI measurements within short time intervals at the time of budding and needle expansion growth (i.e., in early spring) and close to the LAI peak, when the twig growth has been completed. The reason was that after reaching the seasonal maximum, no significant differences between subsequently obtained values were found in the following 2 months. Therefore, we recommend this period for the estimation of seasonally representative LAI values, enabling the comparison of various spruce stands. The maximum hemi-surface LAI value reached 12.4. Based on our results, the most effective LAI values for maximum above-ground biomass production were within the range of 10–11. We found an LAI over these values to be less effective for additional production of above-ground biomass. In forest practice, thinning intensity is mostly described by percentage of stocking reduction. We want to show that not only thinning intensity, but also the type of thinning is important information. The type of thinning significantly affected the stand above-ground biomass increment, canopy openness, stand LAI and LAI efficiency. The stimulating effect of high-type thinning was observed; the LAE as well as the CPI increased. Low-type thinning had no such effects on LAE increments compared to the high-type thinning with similar intensity.

---

     

Effect of mineral nutrition content on oxygen exchange and chlorophyll a fluorescence in needles of Norway spruce

Photosynthetic O(2) evolution at high irradiances (approximately 600-1000 micro mol m(-2) s(-1)) and O(2) uptake in darkness were measured in needles of control, irrigated and irrigated-fertilized trees of Norway spruce (Picea abies (L.) Karst.). Measurements were made at 20 degrees C and at high CO(2) concentrations. The results suggest that, at given times of the year, a major part of the variation in gross photosynthesis of current-year and one-year-old needles across treatments is associated with differences in needle N content. Furthermore, the rate of O(2) uptake measured after 5 or 10 min in darkness was positively correlated with both the preceding rate of gross O(2) evolution and the N content in fully expanded current-year needles. Measurements of chlorophyll a fluorescence, taken simultaneously with measurements of O(2) evolution in current-year sun needles, showed that Stern-Volmer quenching of minimum fluorescence and the ratio of variable to maximum fluorescence in the dark- and light-adapted state were strongly correlated with the gross rate of O(2) evolution. This suggests that the increased rate of gross photosynthesis in needles of irrigated-fertilized trees was associated with adjustments in the thermal energy dissipation within photosystem II.     

Biophysical controls on rhizospheric and heterotrophic components of soil respiration in a boreal black spruce stand

We conducted a root-exclusion experiment in a 125-year-old boreal black spruce (Picea mariana (Mill.) BSP) stand in 2004 to quantify the physical and biological controls on temporal dynamics of the rhizospheric (R(r)) and heterotrophic (R(h)) components of soil respiration (R(s)). Annual R(r), R(h) and estimated moss respiration were 285, 269 and 57 g C m(-2) year(-1), respectively, which accounted for 47, 44 and 9% of R(s) (611 g C m(-2) year(-1)), respectively. A gradual transition from R(h)-dominated (winter, spring and fall) to R(r)-dominated (summer) respiration was observed during the year. Soil thawing in spring and the subsequent increase in soil water content (theta) induced a small and sustained increase in R(h) but had no effect on R(r). During the remainder of the growing season, no effect of theta was observed on either component of R(s). Both components increased exponentially with soil temperature (T(s)) during the growing season, but R(r) showed greater temperature sensitivity than R(h) (Q(10) of 4.0 and 3.0, respectively). Temperature-normalized variations in R(r) were highly correlated with eddy covariance estimates of gross ecosystem photosynthesis, and the correlation was greatest when R(r) was lagged by 24 days. Within diurnal cycles, variations in T(s) were highly coupled to variations in R(h) but were significantly decoupled from R(r). The patterns observed at both time scales strongly suggest that the flow of photosynthates to the rhizosphere is a key driver of belowground respiration processes but that photosynthate supply may control these processes in several ways.     

Effects of slash retention and wood ash addition on fine root biomass and production and fungal mycelium in a Norway spruce stand in SW Sweden

In the study reported here we examined the short-term effects (1–3 years) of slash retention (SR) and the long-term effects (13–15 years) of wood-ash application (A) on fine roots and mycorrhizae in a 40-year-old Norway spruce forest in southwest Sweden. Soil cores were used to obtain estimates of the biomass (g m⁻²) of roots in three diameter classes (<0.5, 0.5–1 and 1–2 mm), root length density (RLD), specific root length (SRL) and mycorrhizal root tip density (RTD). Fine root (<1 mm) length production and mortality, and mycelium production, were estimated using minirhizotron and mesh bag techniques, respectively. Compared with the control plots (C), the biomass of fine roots in diameter classes <0.5 mm and 0.5–1 mm was significantly higher in A plots, but lower in SR plots. In addition, RLD was significantly lower in the humus layer of SR plots than in the humus layers of C and A plots, but not in the other layers. None of the treatments affected the SRL. In all soil layers, the SR treatment resulted in significant reductions in the number of ectomycorrhizal root tips, and the mycelia production of fungi in mesh bags, relative to the C treatment, but the C and A treatments induced no significant changes in these variables. Fine root length production in the C, A and SR plots amounted to 94, 87 and 70 mm tube⁻¹ during the 2003 growing season, respectively. Fine root mortality in treated plots did not change over the course of the study. We suggest that leaving logging residues on fertile sites may result in nitrogen mineralisation, which may in turn induce reductions in root biomass, and both root and mycelium production, and consequently affect nutrient uptake and the accumulation of organic carbon in soil derived from roots and mycorrhizae.     

Interactions between soil scarification and Norway spruce seedling types

Interactions between scarification treatments and seedling types of Norway spruce were examined at two different locations in southern Sweden. The scarification treatments were not scarified control, mounding and soil inversion and the seedling types were a 10 week-old containerized seedling (mini seedling), a 2 year-old containerized seedling and a 2 year-old hybrid seedling, grown as a containerized seedling the first year and as a bare-root seedling the second year. Site preparation intensity had a greater effect on the mini seedlings. The results indicated that mini seedlings established faster in the soil inversion treatment compared to the larger seedling types. At the same seedling age, the mini seedlings had faster or similar growth rate as the containerized and the hybrid seedlings regardless of scarification treatment. Although mini seedlings grew as well as or even better than larger seedlings if they were successfully established, they were more sensitive to their planting environment and proper handling was critical. Problems with frost heaving and competing vegetation have to be taken into consideration when choosing site preparation method and seedling type.